Here is a direct statement from Mara about when she fought Lumiya. Its pretty vague but her ya go.
That's where I was when a female cyborg found me. She wanted to bring me back to Isard. I didn't want to go. So I didn't. Cyborg got my lightsaber but not me. Better luck next time. - the essential guide to the Force
Lumiya stomped Nelani in the physical clash. Telekinesis is a different story - they were about equally matched, but Lumiya was constantly talking to Jacen rather than focusing on Nelani and ended up being disarmed as a result.
And Mara probably wins. Her blaster didn't do much in her confrontation against Lumiya and I doubt it would do anything against Talon.
The text makes it clear Nelani was outmatched physically.
Lumiya lost Force power as a result of her cybernetics, but her mastery was sufficient to know a myriad of techniques and her Concealment was enough to hide her alignment from Jacen as per his own admission. As I said, she doesn't hold up to these characters Force-wise (in a combative sense), but her lightwhip's unorthodoxy makes up for that in some ways.